1. Field of the Invention
This invention relates generally to coating and coated articles and, more particularly, to methods of depositing coatings and making coated articles having low haze and/or low emissivity. This invention also relates to solar control coating for articles to reduce the transmission of infrared (IR) energy, particularly near infrared (NIR) energy, while maintaining a relatively high visible light transmission and substantially neutral transmitted and/or reflected color of the coated article.
2. Description of the Currently Available Technology
Low emissivity coatings deposited on a substrate, e.g., a glass substrate, are used in many applications, such as see-through freezer doors, oven door windows, architectural windows, e.g., commercial or residential windows, and vehicle windows, to name a few. Emissivity refers to the energy emitting or radiating propensity of a surface. xe2x80x9cLow emissivity coatingsxe2x80x9d allow ultraviolet (UV) energy, e.g., below 400 nm, and visible wavelength energy, e.g., 400 nm to about 780 nm, to be transmitted through a window but reflect infrared (IR) energy, e.g., greater than about 780 nm. Such low emissivity coatings are attractive for use with architectural windows, for example, since they prevent radiant heat loss through the window during cold periods, reducing heating costs during the winter and air conditioning costs during the summer.
Low emissivity coatings, however, are not well suited for use in warmer climates, such as the Southern United States, since low emissivity coatings transmit a high percentage of visible light during the day that can heat the interior of the building, thus increasing cooling costs. Examples of commonly used low emissivity coatings include metal oxides, such as tin oxide (SnO2), or doped metal oxides, such as fluorine (F) doped tin oxide. U.S. Pat. No. 4,952,423 discloses a fluorine-doped tin oxide low emissivity coating.
In warmer climates, coatings which provide not only low emissivity but also solar control properties, such as solar energy reflection or absorption or a low shading coefficient, are desirable. The term xe2x80x9cshading coefficientxe2x80x9d is generally used in the glass industry and relates to the heat gain obtained when an environment is exposed to solar radiation through a given area of opening or glazing to the heat gained through the same size area of a xe2x85x9 inch thick single-pane clear glass (ASHRAE Standard Calculation Method). The xe2x85x9xe2x80x3 thick clear glass is assigned a value of 1.00. A shading coefficient value below 1.00 indicates better heat rejection than the single-pane clear glass and vice versa.
Fluorine doped tin oxide provides low emissivity characteristics. Tin oxide doped with other materials, such as antimony (Sb), can have solar energy reflecting and absorbing characteristics. Antimony doped tin oxide coatings are more highly solar energy absorbing than tin oxide alone. The doping of tin oxide with antimony improves absorption of near infrared solar energy and also decreases the transmission of visible light, characteristics particularly useful in warm climates to prevent overheating of the interior of a building or vehicle in the summer months.
In addition to tin oxide, other metal oxides used in the formation of low emissivity and/or solar control coatings include Sb2O3, TiO2, Co3O4, Cr2O3, InO2 and SiO2. However, tin oxide has advantages over these other metal oxides because of its abrasion resistance, hardness and conductive properties. The advantages of both low emissivity and solar control can be obtained by providing a coating having both a low emissivity coating material, such as fluorine doped tin oxide, with a solar control coating material, such as an antimony doped tin oxide, or by providing a coating having mixed emissivity and solar control materials, such as tin oxide doped with both antimony and fluorine. An example of one such coating is disclosed in GB 2,302,102.
U.S. Pat. No. 4,504,109 discloses an infrared shielding lamination having alternate infrared shield layers and inferential reflection layers.
GB 2,302,102 discloses a coating having a single layer of tin/antimony oxide in which the tin and antimony are in a specified molar ratio, and also discloses a fluorine doped tin oxide layer applied onto a tin/antimony oxide layer.
As a general rule for metal oxide or doped metal oxide coatings, as the coating thickness increases, the emissivity of the coating decreases and the conductivity increases. Therefore, if no other factors were involved, a solar control coating having a low emissivity, e.g., less than about 0.2, could be obtained simply by increasing the coating thickness to a level to provide the desired emissivity. However, increasing the coating thickness also has the disadvantages of increasing the coating haze, i.e., the amount or percent of light scattered upon passing through an object, and of decreasing the amount of visible light transmission. Such coatings may also exhibit undesirable iridescence. Particularly for architectural or vehicle windows, such haze and iridescence are not desired.
For most commercial applications, haze greater than about 1.5% is typically considered objectionable. Therefore, the ability to provide a low emissivity coating with or without solar control properties has thus far been limited by the necessity to minimize the coating haze to commercially acceptable levels.
GB 2,302,102 hypothesizes that such coating haze is due to internal haze caused by the migration of sodium ions from the glass substrate into the coating and proposes providing a non-stoichiometric silicon oxide barrier layer between the glass substrate and the coating to block sodium ion migration to reduce haze.
Many known infrared reflective coatings also exhibit iridescence or interference colors with reflected and transmitted light. Coated transparencies, such as vehicle windows, that provide lower infrared transmittance and lower total solar energy transmittance to reduce the heat gain in the vehicle interior should also preferably be of a substantially neutral, e.g., gray, color so as not to clash with the overall color of the vehicle.
As will be appreciated by one of ordinary skill in the art, it would be advantageous to provide a coating, coated article and/or coating method which provide a relatively low emissivity coating, e.g., a coating with an emissivity less than about 0.2, which also has a low haze, e.g., less than about 2.0%. It would also be advantageous to provide a coating and/or coated article having reduced infrared transmission and/or a low shading coefficient while maintaining a relatively high visible light transmission and reduced iridescence.
A coating of the invention includes a first coating surface, a second coating surface, and a breaker layer located between the first and second coating surfaces. The breaker layer is configured to interrupt the crystalline structure of the coating.
A further coating of the invention includes a substantially crystalline first layer, a substantially crystalline second layer deposited over the first layer, and a breaker layer located between the first and second layers. The breaker layer is configured to prevent or at least reduce epitaxial growth of the second layer on the first layer.
Another coating includes a substantially crystalline first layer including antimony doped tin oxide having a thickness of, for example, about 1200 xc3x85 to about 2300 xc3x85; a substantially crystalline second layer deposited over the first layer, the second layer including fluorine doped tin oxide and having a thickness of, for example, about 3000 xc3x85 to about 3600 xc3x85; and a breaker layer located between the first and second crystalline layers. The breaker layer, e.g., an amorphous layer, prevents or at least reduces epitaxial growth of the second layer on the first layer.
A coated article of the invention includes a substrate and a coating deposited over at least a portion of the substrate. The coating includes a first coating surface and a second coating surface, with a breaker layer of the invention located between the first and second coating surfaces.
A further coated article of the invention includes a substrate, a substantially crystalline first layer deposited over at least a portion of the substrate, a breaker layer deposited over the first layer, and a substantially crystalline second layer deposited over the breaker layer.
An additional coated article includes a substrate, a substantially crystalline first layer deposited over at least a portion of the substrate, and a breaker layer deposited over at least a portion of the first layer. The breaker layer is configured to prevent or at least reduce epitaxial growth of a subsequently deposited substantially crystalline coating layer onto the coated article.
A further coated article includes a substrate, a color suppression layer deposited over at least a portion of the substrate, and a first substantially transparent, conductive metal oxide layer deposited over the color suppression layer and having a thickness of, for example, about 700 xc3x85 to about 3000 xc3x85. The color suppression layer is preferably graded, with a thickness of, for example, about 50 xc3x85 to about 3000 xc3x85.
Another coated article includes a substrate, an antimony doped tin oxide layer deposited over at least a portion of the substrate and having a thickness of, for example, about 900 xc3x85 to about 1500 xc3x85, and a fluorine doped tin oxide layer deposited over the antimony doped tin oxide layer and having a thickness of, for example, about 1200 xc3x85 to about 3600 xc3x85. The antimony doped tin oxide layer preferably has at least two stratas of different antimony concentrations, with a first strata having a thickness of, for example, about 985 xc3x85 and a second strata having a thickness of, for example, about 214 xc3x85.
A still further coated article includes a substrate, a first doped metal oxide layer deposited over at least a portion of the substrate, and a second doped metal oxide layer deposited over the first doped metal oxide layer. The first doped metal oxide layer has a lower refractive index than that of the second doped metal oxide layer.
A further coated article includes a substrate, a color suppression layer deposited over at least a portion of the substrate, a substantially crystalline first layer deposited over the color suppression layer, a substantially crystalline second layer deposited over the first layer, and a breaker layer of the invention located between the first and second layers.
An additional coated article includes a substrate, a first coating region deposited over at least a portion of the substrate, the first coating region including a metal oxide and a first dopant; a transition region deposited over the first region, the transition region including a metal oxide, the first dopant, and a second dopant, with the ratio of the first dopant to the second dopant constantly changing with distance from the substrate; and a third coating region deposited over the second coating region, the third coating region including a metal oxide and the second dopant. Optionally, one or more breaker layers of the invention may be interposed within the coating stack.
A method of coating a substrate includes depositing a substantially crystalline first layer over at least a portion of a substrate, depositing a breaker layer over the first layer, and depositing a substantially crystalline second layer over the breaker layer. The breaker layer is configured to prohibit or reduce epitaxial growth of the second layer onto the first layer.
Another method of coating a substrate includes depositing a substantially crystalline first layer over at least a portion of a substrate, and depositing a breaker layer over the first crystalline layer. The breaker layer is configured to prevent or at least reduce epitaxial growth of a subsequently deposited crystalline layer onto the first crystalline layer.
A further method of forming a coated article includes providing a substrate, depositing a color suppression layer over at least a portion of the substrate, the color suppression layer having a thickness of, for example, about 50 xc3x85 to about 3000 xc3x85, and depositing a first substantially transparent conductive metal oxide layer over the color suppression layer, with the first conductive metal oxide layer being, for example, antimony doped tin oxide having a thickness of, for example, about 700 xc3x85 to about 3000 xc3x85.